Onan 20 KW generator won't start - Has to be electrical

1993 vintage with Cummins 4cyl diesel, 1,600 hours. This is generator 1. Ran perfectly always until it sat for months on the hard, now back in the water, it ran for 20 seconds and hasn't run since.

Figured it had to be fuel and prime related, but now it's getting excellent fuel flow, turns over perfectly, but refuses to start....not even a hint of starting.

I now think it's electrical.....reason being the oil pressure gauge is dead as door nail during cranking, bought new oil pressure send unit, made no difference, checked continuity on the sensor fault red reset button (which never popped out but have read they can go bad regardless) and it's fine.

Connected mechanical oil pressure gauge and get readings of 50 psi when cranking.....so have excellent oil pressure. And yet the fact that the electrical oil pressure gauge does not budge tells me something electrical not right preventing it from starting,

Another clue, when attempting starting from lower helm a little green light comes on the working generator 2 during cranking and stays on after the generator 2 stays running.

But when cranking generator 1, the green light does not come on during cranking...even though it will turn over just fine from that helm toggle...just refuses to start (And obviously no light during running either since it won't run !)

Any ideas ?.

sounds like your on the right path. Now just get another pair of hands to crank the engine while you use a meter to see if power is coming to the genny. That will at least tell you which direction to start looking.

Thanks. Since it cranks perfectly there is power but presume you mean power to somewhere else on the generator.. like the electronics ? Where exactly to check that ?

Naturally Gen 1 has a water maker support right above the electronics box and is nearly impossible to get to ! (Generator 2 has no such obstructions)

Check that the glow plugs are being energized during preheat/cranking. Check that the fuel solenoid is energized during preheat/cranking. Some fault breakers can open yet not pop the button out, a whack on the panel with a butt of a screwdriver can pop it out and then it be reset.

How did you test the fault breaker without taking the cover off the control box?

To troubleshoot further, should get schematic and work through it methodically. If hardware is in the way of opening control box, move the hardware.

Also, close sea cock while troubleshooting. Lots of cranking can fill muffler and the water can back up into engine. At this point, drain the muffler.

You said fuel is good. Did you check that at an injector??? Fuel solenoid may not be activated.

I expect safety shutdown features to allow it to start then shut down if a fault is detected. Since it doesn't start at all IMO the solenoid and its power supply is where I would look.

If you don't have power at the control panel, that's a clear problem so track that down. Ski gave all the key points.

Had same problem with a Westerbek 4.4-Harness plug was corroded not letting oil pressure sensor signals through. Check your harness for disconnects and check for corrosion.

Ski in NC said:

How did you test the fault breaker without taking the cover off the control box?

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I did not take the top cover off but I can pull out the front panel a couple of inches before the inside wire lengths max out which is enough to get probes to that fault detection breaker and and check continuity.

ddalme said:

Had same problem with a Westerbek 4.4-Harness plug was corroded not letting oil pressure sensor signals through. Check your harness for disconnects and check for corrosion.

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Do oil pressure sensor wires go from sensor to wiring in the Onan electrical box or go beyond that or somewhere else ?

Regardless, I disconnected the oil sender wires from gen 2 last night and was surprised it still started and ran just fine ! There are two more oil pressure sensors for actual shutdown purposes so perhaps I can check the wiring on those with ohm meter.

bayview said:

You said fuel is good. Did you check that at an injector??? Fuel solenoid may not be activated.

I expect safety shutdown features to allow it to start then shut down if a fault is detected. Since it doesn't start at all IMO the solenoid and its power supply is where I would look.

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Yes and fuel solenoid is opening

You can also call Cummins Customer Care and they will step you through a troubleshooting procedure. Have your model, spec and serial number.


800 888-6626

If fuel solenoid is energizing, it should start. Since you were fiddling with the elec fuel pump, system may be air loaded and need to be bled.

Any diesel needs 3 things to start, fuel, heat and compression. Good rings, valves and cylinders will allow enough pressure to build to heat the air above diesels' ignition point. Sitting can contract the rings enough that ignition pressure/temperature isn't reached. Glow plugs help, but a block heater is better. On mine, the glow plugs only work when the start button is pushed, not long enough. I put in a switch so I can manually tun on the plugs.
I have a MDL3 14kw. When the stop solenoid failed, I still had a little fuel dribble at the injectors. Not enough to start.
The oil pressure and coolant temperature safeties are bypassed while the start button is pressed. Normally the engine starts and enough oil pressure is available before you can release the button. So not having oil pressure while cranking doesn't stop the stop solenoid. The engine should make start like noises even if it fails to start.
It also could be an electrical problem like corrosion in connectors in the control box. Check voltage at the stop solenoid while cranking. No voltage, no command to run.
There are relays/solenoids in the control box that could fail, too.
My 3 cylinder is probably similar to yours, near the same age and a Cummings engine. I think 1989.
If you do end up needing a stop solenoid, I bought mine on ebay for about 1/4 of the list price. But any injector pump rebuild company will have the part. Your injector pump should have a id tag with the model number. Mine is a Stanadyne DB2,very common, uses up to 8 cylinder. The internet should have a parts diagram. I'd post the instruction pdf, but it's over Trawlers limit 4.9mb. Send a pm w/email and I'll send it.

ddalme said:

Had same problem with a Westerbek 4.4-Harness plug was corroded not letting oil pressure sensor signals through. Check your harness for disconnects and check for corrosion.

Click to expand...

Well, it sure sounded like a good theory for my gen as well, but as it turns out, I have no visible corrosion......but still, in desperation I tried disconnecting any of the wires from the three oil pressure sensors in working gen 2 ....and it does not keep the oil pressure gauge from working or from the gen from starting.

Also, since I can get to gen 2 top of electronics box pretty easy I tested the gen with many different things disconnected, like diodes, and it made no difference...oil pressure gauge still worked, engine started right up regardless.

Ski in NC said:

If fuel solenoid is energizing, it should start. Since you were fiddling with the elec fuel pump, system may be air loaded and need to be bled.

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Been there, done that (switched good gen primer pump for bad), and did a lot of bleeding....still no action.

Alaskan Sea-Duction said:

You can also call Cummins Customer Care and they will step you through a troubleshooting procedure. Have your model, spec and serial number.


800 888-6626

Click to expand...

Tried that, seemed good at first, but had to go to "level 2" techs....2 hours later still waiting on a call back from Level 2 Premadonnas, that should have taken no more thanl 30 minutes according to Cummuns gal.

So you verified inj pump solenoid is energized when cranking?

Did you prime using the electric and/or mechanical lift pump?

For bleeding did you crack the 17mm nuts on the injectors and then crank?

I had the exact same problem---all looks good but won't start. Broke down and got a generator guy in. He removed the backside of the enclosure. There was a wire there with a simple glass fuse in a holder. He changed the fuse and it started right up. I have no clue what the wire is for but now everything works. My genny is an 8 KW Onan (Kubota motor).

hmason said:

I had the exact same problem---all looks good but won't start. Broke down and got a generator guy in. He removed the backside of the enclosure. There was a wire there with a simple glass fuse in a holder. He changed the fuse and it started right up. I have no clue what the wire is for but now everything works. My genny is an 8 KW Onan (Kubota motor).

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Had the exact same issue and fix with my 8 kw Onan.

hmason said:

I had the exact same problem---all looks good but won't start. Broke down and got a generator guy in. He removed the backside of the enclosure. There was a wire there with a simple glass fuse in a holder. He changed the fuse and it started right up. I have no clue what the wire is for but now everything works. My genny is an 8 KW Onan (Kubota motor).

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Wow...that's amazing. Naturally mine will be nearly impossible to remove the back from...so close to the wall and so much other crap in the way.....but maybe....

mason and cajun....do you mean the exact same problem in every respect ? In other words, did you guys also have separate generator on/off toggle switches at the helm with "on" LED light that stopped working (during cranking) at the same time the oil pressure gauge stopped working....or did you only have electrical trouble at the generator itself ?

(I would already have tried removing the back of the generator sound enclosure to look for this elusive fuse holder, but I won't be back at the boat until Sunday night at best)

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As an aside I did finally hear back from a Cummins Onan "Level 2" tech...who was very nice and emailed me the motherload of troubleshooting manuals... including the elusive one page electrical schematics that shows how it all ties together.

Only problem is the electrical schematics were probably originally drawn on way larger drafting paper and it almost takes an electron microscope to make out the details on the 8.5 x 11 scan !

You posted that you have volts present on the injection pump solenoid. If so, the no start is not an electrical problem. At this point.

Dune said:

Yes and fuel solenoid is opening

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¿Is the fuel shut-off solenoid fully retracting? ¿Are the fuel shut-off linkages not jammed or impaired in any away a move freely when the the solenoid is energised?

To be sure it is not a solenoid or related problem you can manually pull up on the linkages and keep the fuel-shut-off open while somebody cranks the genny.

Ski in NC said:

You posted that you have volts present on the injection pump solenoid. If so, the no start is not an electrical problem. At this point.

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That was according to the Onan mechanic, not me....I don't know how good a mechanic he is yet. He talks a good game but whether he can walk the walk has yet to be determined.

As an aside, can you tell me how to check compression on the 4 cylinders ?

Ski in NC said:

You posted that you have volts present on the injection pump solenoid. If so, the no start is not an electrical problem. At this point.

Click to expand...

OK, back at the boat tonight, and do my own testing, rather than relying on word of mechanic and see their actually is NO voltage at the injection pump solenoid

I connected up a temporary alternative source of 12 volts and the injection pump solenoid does make a clicking sound as expected.

In theory I could probably now run the generator like that but can't, because the mechanic took a part of the injector pump with him to repair !! (He will in theory be back Monday morning [tomorrow] at 9am with the "repaired" part.)

But the question remains, WHY is there no voltage getting to that solenoid ? Any theories ?

As to the mason and Cajun theories of a blown glass fuse, I can get the back sound cover off but the generator is so close to the wall I can't get my head back there enough to to see much of anything ......plus I now have the complete troubleshooting and service manual and there is no mention of such.....I suppose Viking could have done something like that but seems unlikely.

Fixed it. Now you guys get to guess what it was

Hint- it was electrical to panel related and ridiculously simple....but not a blown fuse and not a tripped or defective sensor fault breaker.

Loose connection?

So much for the mechanic who took patr of the injection pump home for repair.

Greetings,
Mr. D. Over rev point set maladjusted?

Glad you found the problem! Could it have been a faulty reset switch?